This invention relates to methods of and apparatus for feeding sheets of material sequentially from a stack, and is more particularly concerned with the separation and feeding of sheets from the bottom of a stack.
Various forms of bottom feeder for stacks of sheet material, such as sheets of paper, are known. These include inter alia U.S. Pat. No. 5,797,597, U.S. Pat. No. 4,336,929, GB2137178A, GB2109352A, EP0459667, EP0446889 and EP0030410. In a number of these prior art machines, the stack of sheets is held in place by a restraining means and one has to adjust the height of the restraining means to define the size of a gap underneath it for the passage of a sheet in dependence upon the thickness of the sheets to be fed. That makes these machines very difficult to set up, as well as requiring readjustment of the restraining means each time that there is a change in the sheets which are to be fed.
It is an object of the present invention to provide a method of and apparatus for feeding sheets of material sequentially from the bottom of a stack in which the means of adjustment necessary in order to be able to feed sheets of different thickness through the mechanism is extremely simple.
It is a further object of the present invention to provide a bottom feeder which is substantially less costly than top feeders but which is reliable in operation and able to feed sheets of different thickness.
It is yet a further object of the present invention to provide a bottom feeder which will feed very thin paper right up to very thick card with only very simple adjustment being necessary.
In accordance with one aspect of the present invention there is provided an apparatus for feeding sheets of material successively from the bottom of a stack of sheets, comprising means defining a suction chamber, one or more perforated belts moveable over the suction chamber, means defining the position of a stack of sheets above the suction chamber so that the stack is in contact with the belt or belts, restraining means for the sheets of the stack positioned towards the downstream end of the suction chamber and arranged to define a gap between the bottom of the restraining means and the belt or belts, and means to produce an upward corrugation in the bottom sheet only of the stack in advance of the restraining means, wherein the profile of the gap is such as to permit the passage of the corrugated bottom sheet.
In accordance with another aspect of the invention there is provided a method of feeding sheets successively from the bottom of a stack of sheets, which comprises generating suction within a suction chamber, moving a perforated belt or belts around the suction chamber thereby to generate a suction force at the surface of the belt or belts, positioning a stack of sheets above the suction chamber in contact with the upper surface of the belt or belts, restraining the forward movement of the sheets towards the downstream end of the suction chamber by restraining means which defines a profiled gap between itself and the surface of the belt or belts, arranging for corrugation means to produce an upward corrugation in the bottom sheet only of the stack in advance of the restraining means, and generating an intermittent suction effect within the suction chamber, thereby to effect feeding of the corrugated bottom sheet of the stack through said profiled gap.
Preferably, the restraining means comprises a gate positioned towards and above the downstream end of the suction chamber which has the capacity for adjustment relative to the belt or belts but which does not need to be adjusted in accordance with the thickness of the sheets to be fed. The only adjustment which needs to be made to accommodate the feeding of sheets of different thickness is an adjustment of the corrugation means in terms of the amount of distortion it produces in the bottom sheet.
The corrugation means is preferably a roller within a single belt and which is capable of adjustment in a direction perpendicular to the direction of movement of the belt, in order to vary the profile of the belt.
Preferably, the restraining means is provided with a recess in a substantially linear bottom edge thereof, in alignment with the corrugation means. This recess is preferably in the form of a notch whose shape mimics the shape of the bottom sheet distorted by the belt. The combination of such a recess and the aligned corrugator means that just by varying the height of the corrugator and thus the amount of distortion of the belt, sheets of a wide range of thicknesses can be fed from the stack without misfeeds or double-feeds. This avoids the need both for repeated setting of the restraining gate and also for careful re-setting of the gap between the restraining gate and the underlying belt.
Preferably, to assist in the separation of the bottom sheet of the stack, and so that only the bottom sheet is held down against the belt, air is blown continuously at the sides of the stack, towards the bottom sheet.